Key to US Polyergus species

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Key to Polyergus species of the United States based on workers, modified from Trager (2013).

1

  • Gastral tergites with pubescence very sparse or lacking, smooth and often strongly shining; North American, most abundant from Atlantic Coast states west to Mississippi Valley (one species extends west to southern Rocky Mountains) (Polyergus lucidus group) =>2
  • Gastral tergites with dense pubescence yielding a silky sheen, obscuring the surface of the integument beneath; Eurasian and North American, in North America from western Great Lakes, prairie and Rocky Mountain states and provinces, to Pacific Coast and Mexican mountains (Polyergus rufescens group) => 7

2

  • Vertex pilose, ½ VeM usually > 10; head and mesosomal dorsum matte and sides at most feebly shining => 3
  • Vertex less pilose, ½ VeM usually < 8; head and mesosomal dorsum matte or shiny; but if matte, then sparsely pilose => 4
    • Host is never Formica dolosa

3

  • Scapes and legs shorter, SI < 105, usually < 100, FI < 140; northern species, New England west to the Dakotas => Polyergus sanwaldi
Head of Polyergus sanwaldi worker
Profile of Polyergus sanwaldi worker
  • Scapes and legs longer, SI > 100, but usually > 110, FI > 140; southern species, North Carolina to Florida, west to Mississippi and southern Missouri => Polyergus longicornis
Head of Polyergus longicornis worker
Profile of Polyergus longicornis worker

4

5

  • Larger and less pilose species, LI of most specimens > 390; ½ VeM 0–1 (very rarely more); eastern Canada to northern Florida, west to Wisconsin, Colorado, New Mexico => Polyergus montivagus
Head of Polyergus montivagus worker
Profile of Polyergus montivagus worker
Head of Polyergus oligergus worker
Profile of Polyergus oligergus worker

6

  • Smaller, shorter-limbed, SL 1.19–1.36, HFL 1.72–2.04; northeastern, Midwestern, and higher altitude Appalachian distribution => Polyergus lucidus
Head of Polyergus lucidus worker
Profile of Polyergus lucidus worker
  • Larger, longer-limbed, SL 1.68–1.79, HFL 2.08–2.44; southern and south central USA and foothill Appalachian distribution => Polyergus ruber
Head of Polyergus ruber worker
Profile of Polyergus ruber worker

7

  • Vertex lacking pilosity or with ½ VeM < 8, usually < 4; pronotal erect pilosity usually all dorsal => 8
    • Hosts in the Formica fusca group, or less often, in the Formica neogagates group, but exclusive of the Formica cinerea complex
  • Vertex notably pilose, ½ VeM > 6, usually 10–30; pronotum always with some erect setae on sides near lower edges => Polyergus breviceps
Head of Polyergus breviceps worker
Profile of Polyergus breviceps worker

8

  • Head and pronotum moderately pilose, ½ VeM < 6 (rarely more), ½ PnM usually > 4; sometimes with infuscated posterior tergites, if gaster appears entirely brown or blackish, ½ PnM > 4 => 9
  • Head and pronotum non-pilose or sparsely pilose, ½ VeM 0, ½ PnM 0–2; distinctly bicolored, head and mesosoma red, gaster entirely dark brown to blackish; western Great Lakes states to Dakotas, Manitoba, usually in moist or bog forests => Polyergus bicolor
Head of Polyergus bicolor worker
Profile of Polyergus bicolor worker

9

  • Scapes fall short of vertex corners by a scape width or more, SI < 85; legs shorter, HFI < 120, usually < 110 => 10
  • Scapes nearly reaching to slightly surpassing vertex corners, SI > 85, usually > 90; legs longer, HFI > 120; coastal hills of southern California and Baja California => Polyergus vinosus
Head of Polyergus vinosus worker
Profile of Polyergus vinosus worker

10

  • Head often and especially sides of mesosoma weakly to conspicuously shining; scapes not reaching vertex corners by about 1.5–2 scape widths, scapes distally clavate, SI 65–82, but usually < 77; legs shorter, HFI 99–120 (but usually < 113 and always < 110 in southern Arizona and Mexico); upper elevation conifer forests of Mexican mountains, north to British Columbia, Rocky Mountain and Plains states, east to Mississippi Valley => Polyergus mexicanus
    • Hosts are a wide variety of high elevation or northern Formica fusca and Formica neogagates group species
Head of Polyergus mexicanus worker
Profile of Polyergus mexicanus worker
  • Head and mesosoma typically entirely matte, or at most weakly shining; scapes longer, not reaching vertex corners by 1.5 scape widths or often less, scapes thickened distally, but at most weakly clavate, SI 75–86, usually > 79; legs longer, HFI 108–121, usually > 115; HD, Mexico north to lower elevations of southern Arizona mountains in oak or mesquite woodlands => Polyergus topoffi
Head of Polyergus topoffi worker
Profile of Polyergus topoffi worker

References

  • Trager, J.C. 2013. Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini). Zootaxa 3722, 501–548.